The output bit rate of video coding is tied to image contents, coding modes, quantization parameters, and so on. Generally, the output bit rate of video coding constantly changes. Transmission bandwidth and storage capacity are known, but the output bit rate of video coding constantly changes, so the contradiction requires bit rate control for regulation.
There are generally two bit rate control methods: a Constant Bit Rate (CBR) control method and a Variable Bit Rate (VBR) control method. The CBR serves the stability of bit rate, and the VBR serves the stability of bit rate quality. When the above two bit rate control methods set the bit rate,
1. the CBR is usually used for setting an average value of the bit rate; and
2. the VBR is usually used for setting an upper limit value of the bit rate.
In the practical application process, both the two bit rate methods have some problems.
1. When the average value of the bit rate is set using the CBR, from long time, different time intervals have different requirements on the bit rate. For example, generally the requirement on the bit rate during the day is higher than that at night; at this time, setting the average bit rate value high will cause wastes, but setting it low will influence the video quality of some time intervals.
2. When the upper limit value of the bit rate is set using the VBR, the VBR control method does not cause the waste of bit rate while guaranteeing the overall video quality. However, the specific storage capacity cannot be previously estimated; when a storage space is configured, it is always configured according to the upper limit value of bit rate, which increases the cost.
The actual transmission bandwidth and storage capacity are limited, but both the existing two bit rate control methods and a bit rate setting method cannot balance the relation between the video quality and the target bit rate.